This explanation may be incomplete or incorrect:Still needs a review and the picture without the labels needs an explanation. Do NOT delete this tag too soon.If you can address this issue, please edit the page! Thanks.

The comic claims that the reason that eclipses don't happen every month is simple to understand by looking at an orbital diagram. Ironically, the cartoon has so many parts and labels that it is far more difficult to understand than is implied. While the graph itself is based on astronomical definitions, all the labels are nonsense in this context. In effect, the comic is a new take on a common joke in which a person asks a scientist a question, the scientist begins by saying "It's really quite simple", then proceeds to give a very lengthy and highly technical explanation that non-scientists would not be expected to understand. Diagrams for eclipses commonly include things that laypeople may not find relevant, without explanation, such as the umbra and penumbra.

All of the labels in the diagram are complicated words or phrases. Some are related to orbital mechanics (e.g. "equinox" and "perihelion"), while others are wholly unrelated or even made up. Each label is nonsensical in its place in the diagram. Compare/contrast with the standard Kepler Orbit diagram.

The title text references warnings to not look directly into the sun, but parodies those warnings by referring to 'orbit', the anatomical term for the eye socket.

All items are not drawn to scale. Neither the sizes of the celestial objects are that similar as shown nor the orbits are. The real scales are shown in this table:

real (in km)

to scale

Sun (radius)

695,700

basketball

distance Earth-Sun

149,600,000

length of a large truck (26 meters)

Earth (radius)

6,371

pinhead (1 mm)

Moon (radius)

1,737

pin (0.3 mm)

distance Earth-Moon

384,399

small necklace (6.6 cm)

When the distance Sun-Earth is scaled to one meter or below neither Moon nor Earth can be seen by the human eye.

Arctangent

Arctangent is the inverse function of the tangent function of trigonometry. You can determine a non-right angle of a right triangle by taking the arctangent of the length of the opposite side divided by the length of the adjacent side.

The angle shown in the comic has no astronomical meaning.

Astral plane

The Astral plane is a plane of existence in various esoteric theories. It features prominently in Dungeons & Dragons cosmology, connecting the various other planes of existence.

The picture shows the lunar orbital plane, the plane in which the Moon orbits the Earth, tilted about 5.1 degrees from the ecliptic.

Declension

Declension is the inflection of nouns in a language. In Latin declension and declination are both called Declinatio. In this comic, however, it might be a portmanteau of declination and (right) ascension.

In astronomy, the declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system. It is measured north or south of the celestial equator, like the geographical latitude on Earth. But in the picture the label is at the angle for the axial tilt of the Earth.

And the right ascension is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question.

Determinant of the date of Easter

In Western Christianity Easter always falls on the first Sunday after the first ecclesiastical full moon after the beginning of spring (equinox). The ecclesiastical full moon is determined by a calendar that approximates the actual time of the full moon, Thus the date of easter is defined by a combination of a solar and a lunar calendar. The position of that angle isn't that bad but it should be not more than 30 degrees (slightly more than one month.)

In mathematics, the determinant is a function of numerical matrices. In this context, however, it apparently refers to something that directly determines the date of Easter.

Dimples of Venus

The Dimples of Venus are indentations sometimes visible on the human lower back.

In astronomy the Belt of Venus is a shadow cast by the Earth visible in its atmosphere.

Enceliopsis

Enceliopsis are small genus of flowering plants in the daisy family, appropriately known as "sunrays".

In astronomy this point has also no specific meaning. But Enceladus is a moon around Saturn.

An Equinox is one of two instants in the year when the sun is exactly over the equator; the length of day and night are very nearly equal that day at all locations on the planet, and it is potentially the first day of Spring or Autumn, depending on the time of year, in which hemisphere (Northern vs Southern) the observer is located, and which definition of seasons one uses.

A Solstice is one of two instants in the year when the sun's angle is maximally far from Earth's equator; when one occurs, the length of the day or night is shortest or longest (depending on whether one is in the northern or southern hemisphere), and (in the United States) it marks the first day of summer or winter.

Both types occur because the Earth's rotation axis is tilted (at 23.4 degrees) from its orbital plane (ecliptic) about the Sun.

Jokingly insisting that two different terms are American/British variants of the same word has been the topic of 1677: Contrails.

Hypothecate

Hypothecate is a legal verb that means something similar to "make a mortgage".

The hypotenuse is the longest side of a right-angled triangle. Here it is an unrelated length, approximately equal to the diameter of the sun (half the angular size of the sun times twice the distance to it).

Obsequity

Obsequity means the state of being obsequious (showing an indecorous willingness to obey or serve, or "sucking up").

Solar is an adjective referring to the Sun, the star in our solar system.

Tropopause

The Tropopause is the boundary in our atmosphere between the troposphere and stratosphere, defined as the boundary where air ceases to cool with increasing elevation. It is 9-17 km above sea level, not the thousands of kilometers as depicted here.

The label appears to point at the orbit of the moon.

Angle between the Astral and the Sagittal Planes

The angle depicted is the inclination of the moon orbit. The planes are marked with nonexistent symbols, derived from Greek letters. The lunar orbit plane is labeled by a mixture of a nu (ν) and a gamma (γ), the ecliptic is labeled with a double chi (χ), and the angle between is marked with a phi (ϕ) but having two vertical lines.

Errata

Errata are corrections in a published text (e.g. a newspaper article) issued after the publication.

The angle depicted lies between the direction from Earth to the Sun in the ecliptic and the line where the lunar orbit plane crosses the ecliptic. When this angle would be zero AND the Moon is between the Sun and Earth a total eclipse would occur. This is they only part of the diagram fulfilling slightly Randall's promise on top of the picture.

[edit]Explanation for "Why isn't there a (solar) eclipse every month?"

If the plane of where the Earth orbits the Sun and where the Moon orbits the Earth were completely aligned, then there would be a solar eclipse at every new moon (once every 29.5 days) and a lunar eclipse at every full moon (half a lunar period about 14.7 days after a New Moon). However, the plane in which the Moon orbits the Earth is tilted with an inclination of 5 degrees relative to that of the ecliptic plane (the plane defined by the Earth's orbit around the Sun). Eclipses are only possible during two eclipse seasons each year (half a year apart) where for a period of 31 to 37 days the Sun is nearly aligned with the two points in the tilted Earth-Moon plane where the Moon crosses the ecliptic plane. During an eclipse season at the time of a new moon there will be solar eclipses visible from certain locations and during full moons there will be lunar eclipses.

The real explanation of eclipses is evident from this xkcd comic, but is labeled with a fictional character similar to a Greek phi but with two vertical lines; the remaining labels also do not contribute to this explanation and exist only to distract or misinform or entertain the reader.

[The plane of the Moon is pictured in a small angle to the Earth's plane and named Astral Plane. The angle is presented between two lines (Greek Nu or Gamma and a double Greek Chi) and identified by a character that looks similar to a Greek Phi but with two vertical lines.]

[The labels at the Moon's path are:]

Tropopause, Prolapse, Errata.

[An arrow points to the Earth at the zero meridian on the equator. The label reads:]

Discussion

I guess first off, we should note the "solstice" is *not* the Bristish equivalent of "equinox" -- they are actually opposites. The equinoxes occur in April and September, when the day & night are equal length, and the solstices occur in June and December, when the length of daylight and nightime, respectively, are at their longest. JamesCurran (talk) 15:30, 18 August 2017 (UTC)

Technically, the opposite of solstice is the other solstice. Solstice and equinoxes are orthogonal. -- Hkmaly (talk) 00:01, 20 August 2017 (UTC)

Being picky but the Equinox/Solstice section refers to equinoxes marking the start of either spring or autumn, but actually both equinoxes mark the beginning of both spring and autumn in opposite hemispheres. ExternalMonolog (talk) 22:08, 22 August 2017 (UTC)

"Determinant of the date of Easter" refers to the fact that in the Catholic Church (and possibly other Christian denomiations) the date of Easter is the first Sunday after the first full moon of Spring, which means it is an astronomical calculation, but completely unrelated to the indicated angle. JamesCurran (talk) 16:28, 18 August 2017 (UTC)

Well, everyone celebrates Easter on the same day, right? So it's the first Sunday after the first full moon for everybody. Berets (talk) 23:20, 18 August 2017 (UTC)

No, not all denominations agree on the date of Easter; a particular example being the Orthodox church, which usually has Easter a week after the Catholic church, but sometimes as much as five weeks later. The difference is caused by the two denominations using different idealized calendars, both lunar and solar, as well as a slight difference in the definition. 162.158.69.57 18:41, 19 August 2017 (UTC)

That supplementary planes humorously refer also to Astral planes as mentioned in this explanation.--Dgbrt (talk) 19:54, 18 August 2017 (UTC)

Solstice comes from the Latin ... Sol = Sun .. Sistere = Stand still. It literally means the day the sun stands still and refers to the longest day of the year (summer) and the shortest day of the year (winter). So how does the Sun "stand still". On those days the Earth reaches either end of orbital ellipse and returns around the other side. If you stick a pole in the ground and observe its shadow every day at Noon you will see the shadow grow longer every day from winter to summer and grow shorter every day from summer to winter. The shadow is shortest when the Sun is highest in the sky at mid-summer and the shadow is longest when the sun is lowest in the sky at mid-winter. The sun is either getting higher in the sky or lower in the sky every day. When the Earth is at the end of the ellipse and the transition takes place the shadow will not make any noticeable change from one day to the next and one could say that the "Sun has stood still". Rtanenbaum (talk) 19:36, 18 August 2017 (UTC)

I think that Solstice/Equinox thing is a reference to Randall having a hobby of spreading linguistic misinformation, as seen in 1677:Contrails.
172.68.26.251 00:32, 19 August 2017 (UTC)

I'm not sure what the labels of the planes are, but they certainly aren't Greek letters. They look like alchemical symbols to me.
162.158.74.243 00:56, 20 August 2017 (UTC)

Part of the humor of Declension is that it's a portmanteau of right ascension and declination. Right now only declination is mentioned. 162.158.75.40 02:43, 20 August 2017 (UTC)

Arctangent is also a music festival in the UK, happening when this comic came out. --162.158.234.46 22:30, 21 August 2017 (UTC)

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